These teachings relate generally to magnetic field sensing, and, more particularly, to directional magnetic field sensing.
Magnetic field sensing is utilized in a wide array of end-applications including linear and rotary motion sensing, magnetic switches, current sensors, and compassing. These sensors find use in automotive, industrial, medical and consumer end-markets.
Magnetic field sensors may operate by inductive coupling or direct magnetic coupling between a localized magnetic or geomagnetic field and a ferromagnetic or semiconducting magnetic sensor material. These sensors may utilize a variety of sensing methods, including the Hall-effect, anisotropic, giant or tunneling magneto-resistive effects among others.
Sensors may be designed to couple to magnetic fields in a single orientation or in multiple orientations. Sensor may utilize ferromagnetic flux-concentrators to improve the coupling of external magnetic fields to the sensor. This increases the magnetic field injected into the sensor and boosts the sensor response.
The use of a single planar flux-concentrator to inject external magnetization into horizontal and vertical semiconductor Hall-effect magnetic sensors has been previously described as well as the use of a ring or disc shaped planar flux concentrator. The use of a planar flux concentrator and a MEMS electrostatic actuator to change the positional coupling of the flux-concentrator to the sensor, modulating the flux-coupling has also been previously described. The use of a flux-concentrator/flux-shield combination in a Wheatstone bridge sensor configuration, wherein two bridge resistor elements are shielded reference magneto-resistors and two bridge resistor elements are sensing magneto-resistors has been previously described. The (multilayer GMR) elements are differentially processed to obtain a net signal output. The flux-concentrator, in proximity to the ends of the magneto-resistor element, provides signal gain.
One drawback of each of these flux-concentrator designs is that they provide generalized magnetic field concentration with little specific vector selectivity. The round or disc-shaped flux concentrators collect magnetization from numerous or all vector orientations. While this does boost signal it does not boost specific vector orientation signals essential for many magnetic sensing applications.
Additionally, generalized proximity of the conventional flux-concentrator designs does not provide the maximum potential flux-coupling possible with fully proximate designs. Thus, maximum signal gain or increased sensitivity is not obtained with prior-art designs.
There is a need for designs that provide both increased directionality and proximate coupling desirable for improved directionality and sensitivity magnetic field sensors.